The dosing and forward feeding of the components is commonly carried out by means of piston pumps, which causes the hoses to enter into a self oscillating state at the forward and reverse action of the pump piston. A remaining pulsation is obtained which leads to an exact dosing being impossible, particularly if the dosing quantity is very small, which is the case e.g. at thermosetting plastic extrusion, where the setting agent only constitutes about 1-4 volume-%. Even at shut-off the extrusion head the hose is somewhat extended, which contributes to incorrect dosing.